Parse custom attribute value blobs for dependencies and rewrite type name strings by Copilot · Pull Request #127596 · dotnet/runtime

Copilot · 2026-04-30T05:21:33Z

Description

CustomAttributeNode had two TODOs: it wasn't parsing the custom attribute value blob for dependencies, and it wasn't rewriting type name strings that could become stale after trimming removes type forwarders.

Dependency analysis (`GetStaticDependencies`)

Decodes the custom attribute blob via CustomAttributeTypeProvider and reports dependencies for:

typeof() arguments
Enum types (needed for boxing)
Property setters and fields referenced in named arguments
Non-primitive array element types

Constructor resolution uses TryGetMethod instead of try/catch, with a null constructor triggering an early return before named argument processing. GetDependenciesFromPropertySetter uses GetTypeDefinition() to correctly resolve property setters on generic attribute types. Dependency decode failures set an instance _isCorrupted flag so rewrite can avoid re-processing known-bad blobs.

Blob rewriting (`WriteInternal`)

RewriteCustomAttributeBlob reads the custom attribute blob manually with BlobReader, writes into writeContext.GetSharedBlobBuilder(), and rewrites only serialized type-name strings where needed (System.Type payloads and enum type names). Type-name resolution uses GetTypeByCustomAttributeTypeName(..., throwIfNotFound: false) and rewrites only when resolution succeeds, preserving unresolved serialized type names as-is.

Rewrite early-outs to copying the original blob when _isCorrupted is set or when the constructor cannot be resolved.

Type safety improvements

NodeFactory.ReflectedType, ReflectedMethod, and ReflectedField now return DependencyNode directly instead of object, since all return paths produce a DependencyNode (either a real definition node or NullDependencyNode.Instance). This removes the need for is DependencyNode pattern checks at all call sites. Similarly, the value is ImmutableArray<CustomAttributeTypedArgument<TypeDesc>> pattern check in GetDependenciesFromCustomAttributeArgument has been replaced with a hard cast, relying on the System.Reflection.Metadata contract that DecodeValue always produces ImmutableArray<...> for SzArray-typed arguments (the value is null case is already handled earlier).

Validation

dotnet build src/coreclr/tools/ILTrim.Core/ILTrim.Core.csproj
dotnet test src/coreclr/tools/ILTrim.Tests/ILTrim.Tests.csproj --filter "FullyQualifiedName~AttributesTests"
parallel_validation (Code Review + CodeQL)

…ame strings Implement custom attribute blob parsing in CustomAttributeNode: 1. GetStaticDependencies now decodes the custom attribute value blob and reports dependencies for typeof() arguments, enum types, property setters, and fields referenced in the blob. 2. WriteInternal now re-encodes the blob with type name strings resolved to their definitions, handling cases where trimming drops type forwarders (e.g. re-encoding "System.Object, System.Runtime" to "System.Object, System.Private.CoreLib"). Remove 24 tests from ILTrimExpectedFailures.txt that now pass. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f4173cc7-fd45-4a62-9a1c-1a31c06cc85b Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

… remove unused parameter - Catch TypeSystemException and BadImageFormatException instead of base Exception - Add DependencyNode type alias to reduce verbose fully-qualified type names - Remove unused isFixedArg parameter from WriteArgumentValue - Hoist constructor resolution out of named argument loop - Fix duplicate CustomAttributeTypeNameFormatter allocations Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f4173cc7-fd45-4a62-9a1c-1a31c06cc85b Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

dotnet-policy-service · 2026-04-30T05:48:50Z

Tagging subscribers to this area: @agocke, @dotnet/illink
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… BlobBuilder Use BlobEncoder.CustomAttributeSignature with FixedArgumentsEncoder and CustomAttributeNamedArgumentsEncoder instead of manual byte writing. Use writeContext.GetSharedBlobBuilder() following established patterns. Removed byte[] materialization - writes directly to shared BlobBuilder. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/d078b767-9d76-41e5-9168-8f6651786108 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

…bute blobs Remove CheckArgumentsForRewrite/CheckArgumentValueForRewrite that skipped rewriting when no typeof() references were found. Always rewrite to exercise the encoding logic and surface bugs. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/46e2e54d-5313-4538-8274-c5cfe241e547 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

…pe.Category - Replace early returns with cascading if/else if/else in EncodeNamedArgumentType, WriteLiteralValue, and WriteScalarValue. - Switch on type.Category instead of type.UnderlyingType.Category in EncodeElementType, handling IsEnum and System.Type in the default case. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/683a21bb-4e07-4219-81e8-b0a320967bd3 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/6129cc2c-9d66-4f42-876a-056fcef7f711 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

MichalStrehovsky

@copilot

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/20d7918c-7976-4a3d-882f-8aac8f4ade8b Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f536fc71-012c-4ae8-b43e-0abb314fd4c0 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

MichalStrehovsky

@copilot

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MichalStrehovsky

@copilot

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MichalStrehovsky

@copilot

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/6f52143b-ce97-4011-8d73-52d18ba9700c Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Co-authored-by: Michal Strehovský <MichalStrehovsky@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

…ewrite Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/5aad31ca-3463-4605-90a7-54c2be91deb6 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Copilot · 2026-05-13T06:49:56Z

@MichalStrehovsky I've opened a new pull request, #128122, to work on those changes. Once the pull request is ready, I'll request review from you.

sbomer

I wonder whether some of the is checks throughout this code should fail fast instead? Seems like hard casts could catch future holes if we don't expect these checks to fail. Otherwise LGTM!

MichalStrehovsky

@copilot

… hard casts instead of is-checks Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/bba68476-9f61-4c82-9f8b-156ddb87c9ba Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/bba68476-9f61-4c82-9f8b-156ddb87c9ba Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Copilot AI and others added 2 commits April 30, 2026 04:17

Copilot AI assigned Copilot and MichalStrehovsky Apr 30, 2026

Copilot AI requested review from Copilot and removed request for Copilot April 30, 2026 05:21

Copilot created this pull request from a session on behalf of MichalStrehovsky April 30, 2026 05:21 View session

github-actions Bot added the area-NativeAOT-coreclr label Apr 30, 2026

MichalStrehovsky added area-Tools-ILLink .NET linker development as well as trimming analyzers and removed area-NativeAOT-coreclr labels Apr 30, 2026

MichalStrehovsky reviewed Apr 30, 2026

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Copilot started work on behalf of MichalStrehovsky April 30, 2026 08:41 View session

Copilot AI requested review from Copilot and removed request for Copilot April 30, 2026 09:04

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MichalStrehovsky reviewed Apr 30, 2026

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Comment thread src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/CustomAttributeNode.cs Outdated

Copilot started work on behalf of MichalStrehovsky April 30, 2026 11:59 View session

Copilot AI requested review from Copilot and removed request for Copilot April 30, 2026 12:08

Copilot finished work on behalf of MichalStrehovsky April 30, 2026 12:09

Copilot AI requested a review from MichalStrehovsky April 30, 2026 12:09

build-analysis Bot mentioned this pull request Apr 30, 2026

Unable to pull image from mcr.microsoft.com #117164

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MichalStrehovsky reviewed May 1, 2026

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Comment thread src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/CustomAttributeNode.cs Outdated

Comment thread src/coreclr/tools/ILTrim.Core/DependencyAnalysis/TokenBased/CustomAttributeNode.cs Outdated

Copilot started work on behalf of MichalStrehovsky May 1, 2026 11:16 View session

Copilot AI review requested due to automatic review settings May 1, 2026 11:23

Refactor CustomAttributeNode rewrite helpers to instance methods

d4b6451

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/6129cc2c-9d66-4f42-876a-056fcef7f711 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>